1. Technical Field
The present invention generally relates to a refrigerant compressor, and more particularly, to a slant plate type piston compressor, such as a wobble plate type piston compressor having a lubricating mechanism for a piston assembly for use in an automotive air conditioning system.
2. Description of the Prior Art
A wobble plate type compressor disclosed in U.S. Pat. No. 4,594,055 includes a piston assembly having a piston and connecting rod which connects a wobble plate and the piston. The piston is provided with a spherical concavity at its bottom side for receiving a ball portion formed at one end of the connecting rod. After receiving the ball portion, a bottom end peripheral portion of the spherical concavity is radially inwardly bent by using a caulking apparatus to firmly grasp the ball portion; however, the ball portion is allowed to slidably move along an inner surface of the spherical concavity. Therefore, a slight gap is created between the inner surface of the spherical concavity and the outer surface of the ball portion. The above-mentioned connection is generally called a ball-socket connection.
Accordingly, it is required to supply lubricating oil to the gap to smoothly move the ball portion along the inner surface of the spherical concavity without abnormal wearing of the ball portion. In Japanese Utility Model Application Publication No. 01-71178, a mechanism for supplying lubricating oil to the gap from the cylinder chamber during the compression stroke is disclosed. However, in this Japanese '178 application, during the compression stroke, lubricating oil is supplied to the gap from the piston chamber together with high pressure refrigerant gas. Smooth movement of the ball portion within the spherical concavity is prevented by the undesirable high pressure of the refrigerant gas. Consequently, abnormal wearing of the inner surface of the spherical concavity and the outer surface of the ball portion is experienced.
Futhermore, because of environmental concerns dictating the use of R134a as the refrigerant of the compressor, the above-mentioned defect becomes worse due to the decreased lubricating ability of R134a compared with conventional CFC refrigerants.